It is known to use a fluid, such as water, to rearrange the fibers of a nonwoven fabric to produce a fabric having fibers interconnected to each other. For example, U.S. Pat. No. 3,485,706 discloses a nonwoven fabric of randomly interentangled fibers in a repeating pattern of localized entangled regions interconnected by fibers extending between entangled regions, which does not use a binder material or the like. The process for making such fabric is described as supporting a layer of fibrous material, e.g., a web, batt, etc. of loose textile staple, paper, etc., fibers, continuous filament, etc., or combination thereon on an apertured patterning member and jetting streams of a liquid supplied at high pressure onto the fibrous material to entangle the fibers and form the fabric. This patent discloses the hydroentanglement of continuous filaments having a ribbon-shaped cross-section and of such filaments having a trilobal cross section. The apertured patterning member may be formed of woven screen or a perforated metal plate, with an open area of from about 10% to 98%. The type of process described therein is referred to herein as "hydroentanglement."
U.S. Pat. No. 3,620,903 discloses a nonpatterned nonwoven fabric which can be a blend of at least 20 per cent by weight of staple textile fibers, e.g., polyesters, acrylics, rayon, cotton, etc., and papermaking fibers, e.g., wood pulp and cotton linters, which have been hydroentangled. Exemplified are fabrics formed of tissue grade paper of wood-pulp fibers hydroentangled on a web of polyester textile fibers.
U.S. Pat. No. 4,442,161 discloses the hydroentanglement of wood-pulp and synthetic organic fibers. A layer of wood-pulp fiber is placed on top of a polyester layer and then the layers are hydroentangled using closely spaced jets to produce a nonwoven fabric having one side with relatively more wood pulp near its surface than the other.
It is also known, from U.S. Pat. No. 4,822,452, to form a fibrous web comprising wet-laid staple length natural or synthetic fibers and wood cellulose papermaking fibers on a papermaking machine using a water furnish of the fibers made up with a "nonionic associative thickener" in the absence of a conventional surfactant. The resulting fibrous web is a blend of the above fibers which is substantially uniform in composition across the thickness of the web.
Similarly U.S. Pat. No. 4,498,956 discloses the manufacture of a nonwoven fibrous web from a dispersion of fibers in a foamed liquid. In such method a water-surfactant solution is formed into a foamed liquid containing bubbles of air. The fibers are then dispersed in the foamed liquid to form a foamed furnish which is used to form a wet-laid web.
U.S. Pat. No. 4,783,231 discloses the formation of a nonwoven web of spun bonded continuous synthetic filaments which are crimped and which may have a circular, noncircular or trilobal cross-section.
U.S. Pat. No. 4,753,834 discloses nonwoven webs formed of bilobal monofilaments which, after drawing, are laid down on a moving belt to form the web.
U.S. Pat. No. 4,753,834 to Hagy et al. and U.S. Pat. No. 4,808,467 to Suskind et al. disclose the hydrogentanglement of a nonwoven web formed of a blend of wood pulp fibers and staple synthetic fibers. Such nonwoven webs are disclosed to be produced by conventional wet or dry papermaking methods.
U.S. Pat. No. 4,410,579 discloses a hydroentangled nonwoven fabric of 100% ribbon-shaped polyester staple fibers having improved disentanglement resistance. Such polyester fibers are disclosed as being generally rectangular or oval in shape, and the ratio of the length of the major axis to the length of the minor axis of the fiber cross-section is in the range of 1.8:1 to 3:1. The final nonwoven fabric is formed by hydroentangling an air-laid web of the polyester fibers.
Notwithstanding such improvements in nonwoven fabrics, it still is desirable to provide a nonwoven fabric of higher strength than that obtained by prior methods, which fabrics can be entangled more effectively and which can be produced with lower capital and operating costs.
After considerable effort directed to finding a nonwoven wood fiber/staple synthetic fiber fabric of improved tensile strength I have now found, unexpectedly, that a wet-laid web containing staple synthetic fibers, for example, polyester fibers, having a ribbon-shaped crenulated cross-section responds much better to water jet, hydroentanglement than a web made with fibers having a ribbon-like round or oval cross-section. I also have found that such a hydroentangled web containing such staple crenulated synthetic fibers quite unexpectedly has a better tensile strength, wet or dry, than its counterpart having a round, oval or smooth ribbon-like cross-section. This result was not expected from the data shown in U.S. Pat. No. 4,410,579 (see FIG. 2 thereof which shows that grab strength decreases as aspect ratio increases). Hence, I determined that a wet-laid web containing ribbon-shaped crenulated fibers does not respond to hydroentanglement in the same manner as a web of fibers which have carded or been air-laid and have a round, oval or smooth ribbon-shaped cross-section. In addition to the synthetic staple fiber cross-sectional shape, I have also discovered that the denier of the synthetic fibers has a significant influence upon the physical properties of a hydroentangled fabric. Further, I have found that the wet-laying method of forming the initial web to be hydroentangled significantly improves both the physical properties of the hydroentangled fabric and the effectiveness of the hydroentanglement treatment. Based upon the above findings, I have developed the present invention.